Change Of BMD After Lumbar Surgery And Its Effect On Lumbar Fusion In The Elderly: A Clinical Study

Part one:Incidence and epidemiologic features of osteoporosis in patients received thoracolumbar surgeryObjective:To observe the incidence and epidemiologic features of osteoporosis in patients underwent lumbar internal fixation surgery.Methods:A retrospective analysis of 329 patients over 40 years old who underwent thoracolumbar internal fixation in the Spine Surgery Team 2,Department of Orthopedics,Xijing Hospital from January 1,2015 to January 1,2019.The lumbar spine bone mineral density(BMD)was measured by dual-energy X-ray absorptiometry(DXA)before surgery,and osteoporosis was determined according to the Osteoporosis Diagnostic Criteria of the Chinese Society of Osteopathic Osteoporosis(OCCGS):normal bone mass(T>-1.0 SD),osteopenia(-1.0≥T>-2.0 SD)and osteoporosis(T≤-2.0 SD).Analysis of clinical distribution characteristics of osteoporosis in different genders,ages and diseases.Results:The mean BMD of 329 patients was 0.913±0.199 g/cm~2.There were 137patients(41.6%)with normal bone mass,81 patients(24.6%)with osteopenia,and 111patients(33.8%)with osteoporosis.In patients received spinal internal fixation surgeries,the incidence of osteoporosis was significantly higher in women than in men(41.86%vs18.4%,P<0.001).There was a statistically significant difference in the incidence of osteoporosis between different age groups(P=0.011):in aged 40-50 years,50-60 years,60-70 years,over 70 years,the incidences of osteoporosis in females were 19.4%,36.2%,46.8%,and 60.5%,and in males were 25.0%,17.1%,20.9%,and 10.0%,respectively.Among patients over 50 years of age,the overall incidence of osteoporosis in females was46.7%,and that in males was 17.3%.At the same time,the incidence of osteoporosis in different spinal diseases was significantly different:the incidence from high to low were82.6%(compression fractures),41.2%(degenerative scoliosis),39.5%(lumbar spinal stenosis),39.2%(lumbar disc herniation),37.8%(lumbar spondylolisthesis)in females;and 80.0%(compression fracture),29.0%(lumbar spinal stenosis),23.1%(lumbar spondylolisthesis),20.9%(lumbar disc herniation),14.3%(degenerative lumbar spondylolisthesis)in males.Conclusion:The incidence of osteoporosis was higher in patients over 50 years old who underwent lumbar internal fixation.The ratio in female patients was significantly higher than that in male patients,and it increased rapidly with age.The incidence of osteoporosis was also significantly different among different spinal diseases.The incidence of Lumbar vertebral compression fracture was significantly higher than that of lumbar degenerative disease(lumbar disc herniation,lumbar spinal stenosis,lumbar spondylolisthesis,etc.).Therefore,patients who plan to receive internal fixation surgery should assess bone quality before operation and receive anti-osteoporosis treatment if necessary.Part two: Change of BMD after lumbar surgery and its effect on lumbar fusion in the elderly.Purpose: To observe the trend of bone mineral density(BMD)and its effect on spinal fusion after lumbar internal fixation and fusion in elderly patients.Methods: A total of 82 patients who underwent lumbar posterior fusion surgery(with internal fixation fusion limited to L4~S1)and who underwent regular follow-up and obtained lumbar spine BMD and imaging data were collected from January 2014 to December 2018.All patients underwent DXA to measure BMD(mg/cm2)from L1 to L4 preoperative.Follow-up was performed at 5 time-points: 3 months,6 months,12 months,24 months,and 36 months postoperatively.Lumbar spine X-ray or CT scan were performed at the follow-up,and the SUK fusion criteria were used to determine whether spinal fusion was obtained.Meanwhile,the adjacent vertebral body above the fusion segments was defined as: 1-level vertebrae,2-level vertebrae,and 3-level vertebrae.Among the 82 patients,55 cases received 3 months of follow-up(group A),46 cases received 6-month follow-up(group B),41 cases received 12-month follow-up(group C),and 32 cases received 24-month follow-up(Group D),26 patients were followed up for 36 months(group E).Lumbar fusion rate was assess in the 41 patients who were followed up for 12 months.BMD changes were analyzed by paired t-test,and the relationship between BMD changes and spinal fusion was analyzed by independent t test.Results: The mean age of the 82 patients was 60.94 ± 8.93 years,and the male to female ratio was 1/1.28(36/46).The mean BMD was significantly lower in the group A,B,and C than the preoperative bone density(P < 0.001,P < 0.01,and P = 0.033).The mean BMD of the three groups was equivalent to 87.70%,93.01% and 93.70% of the preoperative value,respectively,there was no statistical difference in group D group and E.In each group,the BMD changes for adjacent vertebral bodies were also different: compared with preoperative values,BMD of adjacent vertebral body(1-level vertebrae,2-level vertebral,and 3-level vertebrae)in group A and B decreased significantly(P<0.05);the BMD of the 1-level vertebrae,and 2-level vertebrae in group C was significantly lower than that preoperative value(P<0.05).There was no significant difference between the 3-level vertebral BMD and the preoperative value(P>0.05).In the D group,the BMD of the 1-level vertebrae was significantly lower than that of the preoperative(P<0.05),There was no significant difference between the density values in 2-level vertebrae and 3-level vertebrae(P>0.05).There was no significant difference between the vertebral bodies and preoperative BMD in the E group(P>0.05).In the 41 patients who underwent 1-year follow-up,32 patients completed fusion at 3 months follow up,4 patients achieved fusion at 6 months follow up,4 patients achieved fusion at 12 months follow up,and 1 patient underwent revision surgery.In 9 patients who did not complete the fusion at 3 months follow up after surgery,the BMD loss was significantly higher than that in fusion patients(0.114±0.024 g/cm2 vs 0.083±0.013 g/cm2,P<0.001).Conclusions: There was a “fast loss-slow recovery” process for BMD after lumbar internal fixation surgeries: the BMD firstly entered a rapid decline phase(3 months after surgery),then entered the stationary phase(6 to 12 months postoperatively),eventually entered a slow recovery period and gradually returned to the preoperative level(12 months postoperative).Changes of BMD in adjacent vertebral body were disproportionate.The BMD in the most cranial vertebrae recovered to the preoperative level earlier than the others.The bone loss of the patients with fusion failure was greater than that of the patients with successful fusion.Therefore,patients who underwent lumbar fusion should receive anti-osteoporosis treatment to prevent internal fixation failure and non-fusion due to rapid bone loss soon after spinal surgery.